The prior art filter apparatus, which has a bag unit and a resilient gasket, is described in U.S. Pat. No. 5,075,004, issued Dec. 24, 1991. A related application is U.S. application Ser. No. 08/112,727, filed Aug. 27, 1993. Related patents include U.S. Pat. Nos.:
3,771,664, issued Nov. 13, 1973, PA1 4,133,769, issued Jan. 9, 1979, PA1 4,204,966, issued May 27, 1980, PA1 4,259,188, issued Mar. 31, 1981, PA1 4,285,814, issued Aug. 25, 1981, PA1 4,419,240, issued Dec. 6, 1983, PA1 4,460,468, issued Jul. 17, 1984, PA1 4,490,253, issued Dec. 25, 1984, PA1 4,669,167, issued Jun. 2, 1987, PA1 4,842,739, issued Jun. 27, 1989, PA1 4,877,526, issued Oct. 31, 1989, PA1 5,039,410, issued Aug. 13, 1991, PA1 5,045,194, issued Sep. 3, 1991, and PA1 5,075,004, issued Dec. 24, 1991.
The most pertinent reference is the 4,877,526 patent.
The prior art filter apparatus includes a housing, a cover plate, a basket, and a filter bag subassembly. The prior art filter bag subassembly has a single bag unit composed of filter material such as paper or cloth and has a snap ring or steel ring. The prior art filter bag unit is conventionally a three-layer bag unit, which has a first inner layer, a second middle layer, and a third outer layer. This bag unit is made by stitching the layers together, then using a final layer which is made longer in the collar, folding it over the snap ring or steel ring and sewing the collar around the ring.
One of the major problems with the prior art filter apparatus is that the filter bag unit is relatively bulky. Another problem with the prior art apparatus is that the filter bag unit does not provide an adequate bypass seal. A further problem with the prior art filter apparatus is that the filter bag unit is relatively difficult to handle and to install.